Apparatus and method for injection casting



Sept. 13, 1960' Filed 061;. 10, 1957 A. B. SHUCK APPARATUS AND METHOD FOR INJECTION CASTING 1 60 l m L i 59 l 4 L- J v I y .686 20 5 29 21 W "T 18 4s 5] 'l 17 J9 a 571 "2- 4 19 Vacuum 5741' Source INVENTOR. Source, flfihuffl $12140)? n er I fresszu'c Midm 3 Sheets-Sheet 1 Sept. 13; 1960 A. B. SHUCK 2,952,056

APPARATUS AND METHOD-FOR INJECTION CASTING Filed Qct. 10; 1957 3 Sheets-Sheet 2 INVENTOR. flrtkurli Sfzuol liter/leg A. B. SHUCK APPARATUS AND METHOD FOR INJECTION CASTING Filed Oct. 10. 1957 3 .6 R W E w MB 4 w 4 3 ,1 M

APPARATUS AND METHOD FOR INJECTION CASTING Arthur B. Shuck, Wheaton, 111., assignor to the United States of America as represented by the United States Atomic Energy Commission Filed on. 10, 1957, Ser. No. 689,459 4 Claims. c1. 22-210 hired Ste Pa n result in spilling. In valving, contact of the valve with A the molten metal may interfere with the effectiveness of the valve, or the fitting of the mold-to the valve may be diflicult and inconvenient. Similar difliculties have been encountered with valves in vacuum casting.

When the metal being cast contains irradiated uranium or some other highly radioactive material, the casting operation may have to be remotely controlled, and the cleaning up of spilled metal and the replacement or ad; justment of valves will be very difiicul-t. Moreover, the

unworkability of the metal or the need for remote control of working operations will make impossible or difiicult the reduction of large radioactive castings to long objects of narrow section.

An object of the present invention is to provide a method and apparatus for casting that avoid spilling by doing away with pouring and that eliminate the need to replace and adjust valves by keeping them away from molten metal and molds. These desirable results are achieved by a novel scheme of vacuum casting.

A further object is to cast a long object with narrow sections. Such an object may be a long slender rod.

Another object is to cast a long narrow objectfree from surface imperfections so that the need for sizing operations is obviated.

According to the present invention, a long tubular mold open at one end and closed at the other, and a crucible containing a charge are placed in a sealed vessel, the vessel is evacuated, the charge is melted, the open end of the mold is dipped into the melted charge, and gas under pressure is admitted to the vessel to drive the melted charge into the mold to the closed end thereof.

In thedrawings:

Fig. l is a sectional elevation, partly schematic, of the novel casting apparatus of the present invention;

Fig. 2 is a fragmentary sectional View of the crucible of the present casting apparatus and the means for elevating the crucible;

Fig. 3 is a fragmentary sectional view of the molds of the present apparatus and the means for supporting the o ds;

Fig. 4 is a sectional view taken on the line 4-4 of Fig. 5 and showing the application of the present casting method to the making of a composite article having many passages;

Fig. 5 is a plan view of the composite article;

Fig. 6 is an exploded view showing parts of the composite article; and l Fig. 7 is a fragmentary sectional view of the portion in circle 7 of Fig. 4, illustrating a step in the making of the composite article.

The apparatus of the present invention comprises essentially a sealed vessel 10, a plurality of tubular molds 11 therein, a crucible 12 (Fig. 2) vertically movable in the. vessel, a heater 13 surrounding the crucible 12, and connections to the vessel 10 for vacuum and gas under pressure. The vessel 10, with the molds 11 and crucible 12 therein is evacuated; a charge in the crucible 12 is melted, the crucible 12 is moved upwards to submerge the lower open ends of the molds 11 in the melted charge; and gas under pressure is admitted to the vessel 10 to drive the melted charge into the molds 11 as far as the closed upper ends thereof.

The vessel 10 comprises a bell 14, a ring 15, and a base '16. The bell 14 has a lifting member 16a. The lower open end of the bell 14 extends into the ring 15 and is sealed thereto by dipping into a body of solder 17 which is contained in a channeled annulus 18, connected to the inside of the ring 15 by a seal weld. A resistance heater 19 in the annulus 18 melts the solder 17 when the bell 14 is to be removed. Leads to the heater 19 are designated by 19a. The bell 14 is clamped to the ring 15 by a flange 20 on the bell 14, a ring 21, seated on the flange 20 and the ring 15, an annular retainer 22 holding the ring 21 in place, and screws 23 going through the annular retainer 22 and threaded into the ring 15. The ring is welded to the base 16.

The base 16 rests on a support 24 and carries a tubular extension 25 which is welded to the base 16 at a central opening therein and extends through the support 24. In the tubular extension 25 there is positioned a body 26 carried thereby by means of a flanged ring 27 secured to the body 26 in a seal weld and resting on the upper end of the tubular extension 25. The flanged ring 27 dips into a body of solder 28 which is carried in an annulus 29 and acts as a seal between the tubular extension 25 and the body 26. A resistance heater 30 in the annulus 29 melts the solder 28 when the body 26 is to be removed from the tubular extension 25.

The parts of the vessel 10, the annuli 18 and 29, the extension 25, the body 26, and the ring 27 are formed of mild steel. The portions that the bodies of solder 17 and 28 contact are coated with copper.

As shown in Fig. 2, the crucible 12 is a cup having an internal hollow conical protrusion 31 in its base. The crucible 12 is of graphite and is coated inside and outside by thoria, which may be applied by spraying over an initial coating of magnesium carbonate. The crucible 12 rests on a stabilized-zirconia disk 32, which rests on a stabilized-Zirconia base 33, to which is attached a cylindrical heater 34 of tantalum surrounding the crucible 12. The base 33 rests on a steel pedestal 35 attached by a pin 35a to the upper end of a rod 36. The pedestal 35 has a circumferential groove 35]) which is engageable by a tool, not shown, for removing the pedestal 35, base 33, heater 34, disk 32, and crucible 12 together. The rod 36. carries at its lower end a piston 36a which is pneumatically'or hydraulically actuated to raise or lower the rod 36 and the crucible 12 with respect to the molds 11. A bellows seal 36b is connected at its lower end in the piston 36a and its upper end to a ring 36c attached to the body 26.

The height to which the crucible 12 may rise in submerging the lower open ends of the molds 11 in the melted metal inthe crucible is determined by engagement. of a shoulder 36d on the rod 36 with an adjustable stop 37. As shown in Fig. 2, this stop has threaded engagement with the interior of the body 26 and is slidably keyed to an adjusting member 38, and so rotation of this member causes the stop 37 to rotate and to. move up or down. The adjusting member 38, which is rotated by a tool 39 inserted therein, is rotatably supported in the body 26 and is held therein by a removable retainer 40 extending through the body 26 and into a circumferential groove 41 in the adjusting member 38. As a practical matter, the stop 37 will be adjusted only downwards from the position shown in Fig. 2, since the shoulder 36d on the rod 36 would contact the lower end of the member 38, not the stop 37, if the stop were above the position of Fig. 2.

As shown in Fig. 1, the heater 13 is an electric high frequency induction coil that surrounds and is spaced from the cylindrical heater 34. The cylindrical heater becomes very hot from eddy currents generated therein by current of 10,000 cycles/sec. or more flowing in the coil heater 13 and melts the charge in the crucible 12 by radiant heat. stabilizer in permitting the energy loss from the coil heater 13 to be varied. Preferably, the coil is formed of a solid bar or strip of tungsten or molybdenum. The coil is supported in notches in three posts 42 spaced 120 from one another, only two posts being shown. The posts 42 are formed of a ceramic such as magnesium silicate and aluminum silicate and are held upright in cups 45 attached to a table 46. Cups 45 and table 46 are formed of stainless steel having coatings of zirconia or alumina which prevent metal spilled from the crucible 12 from sticking.

Leads 47 and 48, preferably of nickel, are supported vertically in contact with the ends of the coil of the heater 13 in the table 46 by means of insulators 49 and rings 50, the insulators 49 being damped to opposite sides of the table 46 at an opening therein, and the rings 50 being bonded tothe lead 48 and engaging the insulators 49 above and below. The lead 47 goes through the lead 48 and is,.of course, insulated therefrom.

The table 46 has a circumferential flange 51 which prevents metal spilled on the table from flowing off the table. The table is centered in the vessel by the member 38 which fits in a central opening in the table 46 and in a lifting ring 52 which is bonded to the table 46. As shown in Fig. 1,' the table 46 is carried on three The cylindrical heater 34 acts as a.

64 at 120 intervals and extend outwards therefrom through verticalaxial slots 68 in the lifting ring 63 and inclined peripheral slots in 69 in the ring 66. Angular movement of the ring 66, which is produced by manipulation of a piece 70 fixed to the ring 66 causes lifting and lowering of the sleeve 64 and of the tubular molds 11 carried thereby.

The supporting flange 65 on the sleeve 64 carriesan upper pallet 71 through which the tubular molds 11 extend and which support the molds or, more particularly, enlarged closed flattened ends 72 formed on the molds. The molds 11 are supported laterally by a lower pallet 73 through which the molds extend. The lower pallet 73 is supported from the upper pallet '71 in spaced relation therebelow by means of a tubular member74, which iswelded to the pallets 71 and .73. The upper pallet 71 has a threaded connection with a rod 75, in turn connected with a lifting member 76, by means of which the entire assembly of molds 11, pallets 71 and 73, and member 74 may be lifted out of the sleeve 64.

The posts 53, legs 58, ring 58b, tray 59, shelf 62, sleeve 64, and ring 66 are formed of stainless steel. The pallets 71 and 73 and thetubular member 74 are formed of stainless steel, AISA #30, composed of 25 w./o. Cr, 20 w./o. Ni, (w./o. signifies weight percentage) and the balance substantially Fe.

Each tubular mold 11 is formed of a high-silica glass possessing exceptional stabiliql, high softening point, and very high resistance to heat shock, because of a very low thermal expansion. Such a glass may be composed of 96 w./o. silica, 4 W./o. boron oxide, and traces of oxides of aluminum, sodium, iron, and arsenic. The

closed end 72 on each mold 11 may be formed by pinchi which 5% to 33% of U 0 or ThO has been added.

posts 53, spaced 120 from one another, only one post I heater leads 47 and 48 are positioned to plug vertically into copper conductors 56 and 57, respectively, which are insulated from one another. Conductors 56 and 57 extend through an inlet 57a to the container ring 15, which inlet is connected through a pipe 57b and a valve 570 to a vacuum source 57d and to a source 57e of gas under pressure.

The table 46 supports three legs 58, only one-being shown. The legs are spaced 120 from one another and extend into openings in the table 46. The legs 58 get lateral support from reduced extensions 58a of the posts 53 and an incomplete ring or horseshoe 58b. The legs 58 extend through and are secured to the ring 58b, which is incomplete in order tomake room for the heater leads 47 and 48. At intermediate portions oftheir lengths the legs 58 carry and are fixed to an annular tray 59, which supports a channeled ring 60, in turn supporting a resistance heater 61. This heater is cylindrical and surrounds the tubular molds in spaced relation thereto. At their upper ends the legs 58 carry and are fixed to an annular shelf 62. t g

As shown in Figs. 1 and 3, a lifting ring 63 is secured to the annular shelf 62. Within the lifting ring 63 is a sleeve 64 having a supporting flange 65. The sleeve 64 is supported on the shelf 62 by a ring 66 and three pins 67, only two pins being shown. The sleeve 66 embraces the lifting ring 63. The pins 67 are fixed to the sleeve A small quantity of ethyl alcohol is used in both of these coating mixtures to obtain the proper consistency prior to application. The purpose of the interior coating of each mold 11 is to assure that the casting have a good surface and extend through the entire length of the mold. The molds 11 may number twenty-five and be arranged in two circular rows around the tubular member 74.

The charge to be melted in the crucible 12 is formed from highly enriched irradiated fuel elements taken from a fast reactor. These fuel elements or pins, after being removed from their jackets, are pyrometallurgically processed with magnesium oxide or aluminum oxide for i the removal of the volatile and more easily oxidized or slagged constituents. 5% by weight of new metal in the form of pure uranium is added. The charge to be melted finally has the following composition:

Percent by weight (Approximately enriched in U The new rods to be cast in the molds 11 have a diameter of 0144:0001". After being cut to length, the rods will be 14.22" long; the length of the rods as cast will, of course, be somewhat greater t an 14.22, for example, 16".

games Melting and casting procedure The charge to be melted is placed in the crucible 12. The plurality of molds 11 is positioned as shown in Figs. 1 and 3. Then the bell 14 is applied and sealed so that the vessel is sealed.

Now the vessel 10 is evacuated. When the pressure in the vessel is reduced to about 50 microns Hg, the induction heater 13 is turned on to begin induction melting of the charge in the crucible. Heating is continued until the charge melts and reaches a temperature of l250-l400 C., for example, 1340 C., in a period of 1 /2 to 3 hours. In the meantime, the molds 11 will have been heated by the heater 61 to a temperature of 350- 500 C., for example, 450 C. As is to be noted from Figs. 1 and 3, the heater 61 overlaps the sleeve 64 a considerable amount so that the closed ends 72 of the molds 11 will be heated as hot as the other portions of the molds.

Now the vacuum source 57d is isolated from the vessel 10, and the crucible 12 is lifted by the piston 36a until the melted metal in the crucible submerges the lower open ends of the tubular molds 11 an appreciable amount, for example, /2 to A, to the position shown in phantom in Fig. 1. Next the source 70 is connected with the vessel 10 to supply helium or argon to the vessel at a pressure of about 45 p.s.i.a. The resulting pressure dilference, applied suddenly across the walls of the submerged tubular molds 11, is enough to overcome the inertia of the molten metal in the crucible 12 and to cause it to rise in and completely fill the molds 11, where the metal solidifies. The casting cycle is completed about 10 seconds after pressurization with the lowering of the crucible 12 and the remainder of the molten metal therein.

The vesselltl and its contents are allowed to cool for 45 to 60 min. after completion of the casting cycle before the assembly of molds 11, pallets 71 and 73, and tubular member are removed. The cast pins, contracting diametrally on cooling, may sometimes be removed from the molds 11 without damage thereto. Often the molds 11 are broken away from the cast pins by being pulverized in crushing wheels. The cast pins may be sheared or otherwise reduced to desired length. No other machining operation is required; the side surfaces of the pins are finished to size in the casting operation.

The cast pins can be used in stainless-steel jackets with sodium metal serving as thermal bonds between the jackets and the pins. Reference is made to page 19 of Zinn application, Serial No. 437,017, filed June 15, 1954, now U.S. Patent No. 2,841,545, for a disclosure of utility for a nuclear-fuel rod of about the same dimensions as the rod of the present application.

It is also possible to use the present casting method and apparatus in which the tubular molds employed remain as the jackets of the fuel elements. In this event, the tubular molds will be formed of tantalum, vanadium, or zirconium. When the tubular molds remain as fuelelement jackets, the pins are thermally bonded directly to the jackets.

Figs. 4-7 show the application of the casting method and apparatus of the present invention to the forming of a composite metallic article 77, comprising a cylindrical shell 78 of hexagonal shape, an upper end plate 79, a lower end plate 80, a plurality of parallel spaced tubes 81 extending within the shell 78 and secured to openings in the end plates 79 and 80, and a cast mass 82 filling the shell 78 and completely surrounding each of the tubes 81.

The shell 78 and upper end plate 79 may be formed integral with one another from a drawn piece, or they maybe separately formed and soldered or welded to one another. The shell 78 and lower end plate 80 are separately formed and welded or soldered to one another. The end plates 79 and 80 are of hexagonal 8 shape to conform to the hexagonal shape of the shell 78.

As shown in Fig. 6, the shell 78 has three extensions 83, and the lower end plate 80 has three extensions 84. The extensions 83 and 84 are brought together and welded or soldered to form sprues 85, which, as shown in Figs. 4 and 5, extend from three alternate sides of the shell 78. Each sprue 85 comprises a short portion 86 extending radially outwards from the lower end of the shell 78 and a long portion 87 extending from the short portion 86 longitudinally downwardly from the shell 78 and having a beveled open end 88.

The cast mass 82 is placed in the shell 78 by the method and apparatus of the present invention. The composite article 77, without the cast'mass 82, but with the sprues 85, is placed in the sealed vessel 10 of Fig. 1, along with the crucible 12, which is considerably below the position of Fig. 4, so that the ends 88 of the sprues are above the top of the crucibles so as to be free of the charge therein. The vessel 10 is evacuated; then the charge in the crucible 12 is melted, and the empty article 77 is preheated; then the crucible 12 is raised to the position of Fig. 4 so that the sprues 85 dip into the molten charge in the crucible; and then gas under pressure is applied to the vessel 10 and acts against the molten charge to force it upwardly through the sprues 85 into the shell 78. The beveled ends 88 on the sprues 85 facilitate the flow of molten metal into the sprues; the gas in the vessel 10- drives the metal downwards in the crucible 12 and upwards in the sprues 85, and the beveled ends 88 provide a better transition from downward flow to upward flow than would straight ends on the sprues.

After the cast mass 82 completely fills the shell 78 and cools for a suflicient length of time, the composite article 77 is removed from the vessel. Now, as shown in Fig. 7, each sprue 85 and the solidified metal therein are cut off so that only a flap 89 remains, which is bent down and welded or soldered to the lower end plate 88 so as to complete the enclosing of the cast mass 82. This mass is now completely enclosed in the shell 78, end plates 79 and 80, and tubes 81.

The cast mass 82 may have the same composition as the rods cast in the tubular molds 11. In such a case the shell 78, end plates 79 and 80, and tubes 81 are formed of niobium or tantalum. The composite article 77 then is a nuclear-fuel element suitable for use in a nuclear reactor; liquid metal will be passed through the tubes 81 to absorb heat from the cast mass 82.

However, the composite article 77 may be put to other uses if it is formed of other materials. For example, the cast mass 82 may be formed of copper, and the shell 78, end plates 79 and 80, and tubes 81 may be formed of steel. In this case, the composite article 77 is a heat exchanger in the conventional sense; one fluid to be heated will be passed through certain tubes 31 and another fluid will be passed through the remaining tubes 81 to heat the said one fluid.

It is also understood that the invention is not to be limited by the details given herein but that it may be modified within the scope of the appended claims.

What is claimed is:

1. A method of making an object, comprising providing a cylindrical shell of hexagonal shape having end plates with openings and longitudinal tubes welded to the end plates at the openings, the shell having three sprues formed at the juncture of one end plate with thee sides of the cylindrical shell spaced from one another, applying a vacuum to a mass of metal and to the spruw of the shell, melting the metal, inserting the sprues into the molten metal, and applying gas under pressure against the metal to make the same go as far as the end plate away from the sprues and surround each of the tubes.

2. The method specified in claim 1 and further comprising the steps of cutting off each of the sprues and the solidified metal therein except for a small flap of metal in the shell.

3. The method specified in claim 1, the ends of the sprues being beveled to facilitate flow of the molten metal thereinto. 1 1

'4. A one-piece'tubular mold open at one end and closed at the other, the mold being formed of glass composed of 96 w./0. silica, 4 w./o. boron oxide, and traces of oxides of aluminum, sodium, iron, and arsenic, the mold having an interior coating formed from a colloidal suspension of graphite in Water to which 5 w./o. to 33 w./o. of an oxide selected from the group consisting of U 0 and ThO is added.

UNITED STATES PATENTS 

